Master Thesis Defense by Andrea Vang

Title: Linking Large Scale Atmospheric Modes of Variability with Fluctuations in the Atlantic Ocean.

This thesis successfully performed an EOF analysis on MSLP, SST, OHC, Salinity and Current speed, identifying the leading modes of variability. PC time series were used to determine which patterns of variability co-varied with NAO, as well as determining a lag on monthly time scales between the oceanic variables and NAO. A PC regression analysis was performed, where the oceanic variables were regressed onto the NAO. The results from the PC time series comparisons and the PC regressions proved that the SST tripole pattern is closely linked to the NAO and lags the NAO by one month on shorter timescales. This link can also be seen in the OHC with the same time lag. The NAO and SSH were also shown to be closely linked with no time lag. Especially in the North and Baltic Sea, the SSH was strongly positively correlated with the NAO. The zonal current speed was found to be strongly correlated to the NAO around Scandinavia and across the GSR. However, the regression coefficients was not very strong in most places.

Observational data of ocean currents across the GSR and Skagerrak was investigated, to determine if they were affected by NAO index. They were plotted against NAO index, and a linear trend was fitted. The observational data from the FSC volume transport showed a small positive trend with NAO index. The other two currents, NIIC and the IF current, did not show an influence from the NAO. The observational data from Skagerrak showed a small westward trend with NAO index. This was due to the counter current positioned north of the strong eastward current that arose with NAO.

Supervisor: Jens Hesselbjerg Christensen 
Censor: Martin Drews, DTU